1. Field of the Invention
The present invention relates in general to an apparatus and method for converting a gas stream containing hydrocarbons to a reaction product containing at least one carbon atom, and more particularly to an apparatus and method for converting a gas stream containing hydrocarbons, such as methane gas, to a reaction product containing at least one carbon atom by reacting the hydrocarbon containing gas stream with a plasma discharge generated between two electrodes.
2. Background of the Art
Natural gas is an abundant resource available worldwide. Methane gas oftentimes accounts for over 90 mole percent of the hydrocarbon composition of natural gas. Although methane gas is readily available, the transportation, storage, and conversion of methane gas is in many cases not economically feasible. Furthermore, higher level hydrocarbons, such as ethane and ethylene, are more economically desirable than methane. Demands for methanol and ethylene, two target products of natural gas conversion, are large and increasing. In particular, the possibility of producing ethylene from methane has attracted intense industrial and academic interest. However, even with the low cost of natural gas, current methane-to-methanol or methane-to-ethylene technologies are in many cases simply too expensive.
Methane conversion has historically and currently involved steam reformation of methane into a mixture of carbon monoxide and hydrogen with the resultant conversion of the carbon monoxide and hydrogen to oxygenates or higher level hydrocarbons. The steam reformation process is, however, highly expensive and requires a large energy input and elevated operational pressures. Direct oxidative coupling of methane (OCM) to higher level hydrocarbons lowers the cost and energy requirements of steam reformation. The primary limitation of oxidative coupling methane conversion is the fact that methane molecules are highly stable in comparison to any of the products formed during the reaction. The energy required to break the carbon-hydrogen bond in methane is quite high. Moreover, direct methane conversion to higher level hydrocarbons is thermodynamically unfavorable below 800 degrees Celsius. This thermodynamic instability can be overcome through the addition of oxygen; however, the addition of oxygen favors the formation of carbon oxides, such as carbon monoxide and carbon dioxide, rather than the formation of higher level hydrocarbons such as ethane or ethylene.
Therefore, although the conversion of methane by oxidative coupling (OCM) has become an active and productive area of research in the past several years, researchers have been unable to devise a simple and economical system which converts methane into higher level hydrocarbons in a one step process at or about atmospheric pressure. Research performed in the early part of the twentieth century on methane in an electric discharge reactor has led to patents being filed on several processes; namely, the production of various aldehydes from methane and carbon dioxide as well as the formation of formaldehyde from methane and oxygen. A large number of chemicals have been prepared by electrochemical synthesis methods, including via plasma reactions. The potential of clean, low-cost, highly selective and energy-efficient synthesis has been found to exist in those processes involving organic electrosynthesis and plasma-catalytic synthesis techniques. In these plasma techniques, free radicals generated by excitation, dissociation and ionization of gas molecules are essential for the subsequent free radical reactions.
The present invention contemplates the conversion of methane in a high pressure (from about one atmosphere to more than 10 atmospheres) and non-thermal plasma generated by corona discharge. The corona discharge encourages the formation of active methane species by the reaction of methane with charged oxygen or other species created in the corona discharge.
Thus, it is an object of the present invention to provide an apparatus for the one step conversion of a hydrocarbon containing gas stream such as natural gas, to higher level hydrocarbons from about atmospheric pressure to more than 10 atmospheres.
It is a further object of the present invention to provide a method for the conversion of a hydrocarbon containing gas stream, such as natural gas, into higher level hydrocarbons through a one step reaction.
It is yet a further object of the present invention to provide an apparatus and method for the conversion of a hydrocarbon containing gas stream, such as natural gas, into higher level organics containing at least one oxygen atom.
It is still another object of the present invention to provide an apparatus and method for the conversion of a hydrocarbon containing gas stream, into higher level hydrocarbons wherein the apparatus contains a catalyst capable of activating the natural gas, and more particularly methane, for coupling at a relatively low temperature from about ambient temperature to 100-300 degrees centigrade.
These and other objects of the present invention will become apparent in light of the present specification, claims, and drawings.